1579.

William Constable - physician and unwilling spy - is in Plymouth waiting to sail to the New World. The expedition, led by renowned explorers and traders, John Hawkins and Sir Humphrey Gilbert, has already suffered birth pangs.

William's friend, Captain Charles Wicken, is accused of killing the son of a wealthy merchant, but the testimonies appear suspect. When William learns that Wicken is one of Walsingham’s agents he uncovers evidence to suggest the murder and Wicken’s naming are designed to conceal a plot of invasion - backed by Rome and Spain.

The sailing of the expedition's fleet is delayed while this threat is examined. William is despatched to St Malo, the lawless haunt of corsairs, to investigate. His betrothed, Helen Morton, together with the fleet, wait for his return.

Malign forces conspire to prevent William from carrying vital intelligence back to Plymouth.

William must evade enemy agents and unravel a tangle of duplicity if he is to survive - and prevent the invasion.

The second book in the bestselling William Constable spy thriller series, A Necessary Killing is perfect for fans of CJ Sansom, Rory Clements and SJ Parris.

Paul Walker is the author of the William Constable series of Elizabethan spy thrillers. He lives in London.